Some say comparing FreeBSD vs Linux benchmarks is unreliable and is as it were, comparing apples with pears.
For what it’s worth: the Phoronix team has done some FreeBSD 8.0 RC1 vs Ubuntu 9.10 Alpha 6 benchmarking:
Both FreeBSD 8.0 and Ubuntu 9.10 will be included in our upcoming big operating system comparison, but for now we are just focusing upon comparing Ubuntu 9.10 and FreeBSD 8.0, but have also added in FreeBSD 7.2 for reference and to see how the performance of this BSD operating system has changed. With FreeBSD 8.0 we were using the AMD64 DVD of the first release candidate using a stock installation. With Ubuntu 9.10 we were using the x86_64 server CD of the Alpha 6 build. With FreeBSD not shipping with a desktop environment by default, we used the Ubuntu server CD so that both could be tested just from the terminal in a similar environment. All of the FreeBSD and Ubuntu options were left at their defaults. One of the package versions worth noting is that GCC 4.2.1 is used in both FreeBSD 7.2 and FreeBSD 8.0 while Ubuntu 9.10 is using GCC 4.4.1. FreeBSD was also using the default UFS file-system while Ubuntu 9.10 is running with EXT4. Each operating system was tested with its default settings (including any debug options) and packages to test an “out of the box” experience. We will be back with more benchmarks once each of these operating systems have been officially released.
and concludes that,
… more times than not, Ubuntu 9.10 Alpha 6 came out on top compared to FreeBSD — both the 7.2 and 8.0-RC releases. Only in the 7-Zip, C-Ray, John The Ripper MD5, BYTE Unix Benchmark Dhrystone 2, and SQLite tests did FreeBSD outperform Ubuntu Linux. Between FreeBSD 7.2 and 8.0, the newer release generally did better but it had regressed with the 7-Zip, Gzip, MAFFT, and Threaded I/O Tester Read tests. That’s how the story pans out on a dual AMD Opteron quad-core workstation, but shortly we will be back around with our large operating system comparison on different hardware and with the final releases of these different operating systems to see how they compare.
Please note that 1) the inner workings of the two operating systems are different, and 2) neither of the systems are ready for release yet, so a lot of things will change and improve.